The present invention relates generally to mounting arrangements associated with securing accessories to an underlying semi-automatic or automatic firearm assembly. More specifically, the present invention relates to a gas tube assembly, and firearms equipped therewith, wherein the gas tube assembly can be adjusted to achieve a desired alignment of the gas tube relative to a receiver assembly associated with an underlying firearm.
Many firearms that are capable of semi-automatic and automatic operation utilize at least a portion of the gas associated with discharge of the firearm to operate the action of the firearm or to cycle the action of the firearm to eject a spent shell casing and chamber a subsequent round of ammunition. As is commonly understood, semi-automatic operation of the firearm allows discharge of the firearm with each trigger actuation wherein automatic operation of the firearm provides sequential discharge of multiple rounds of ammunition while the trigger remains depressed. It is further appreciated that such firearms can also be configured to operate in a “burst” mode wherein multiple projectiles can be fired with each trigger actuation. Such firearms commonly allow the user to sequentially discharge multiple rounds of ammunition via only interaction with the trigger whereas single round firearms commonly require user operation of a bolt, hammer, or pump action to effectuate discharge of a spent munition casing and chambering of a subsequent round of ammunition.
In gas operation, a portion of high-pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed through either a port in the barrel or trap at the muzzle. This high-pressure gas impinges on a surface such as a piston, a tappet, connecting rod, bolt carrier, or a surface associated with the action or bolt carrier to provide motion for unlocking of the action, extraction of the spent case, ejection, cocking of the hammer or striker, chambering of a fresh cartridge, and subsequent locking of the action. In many semi-automatic and automatically operable rifles, a gas tube extends in a longitudinal direction along a rearward oriented portion of the barrel and is utilized to redirect a portion of the discharge gas stream toward the action to effect the automatic operation of the action to effectuate the automatic operation of the action. Firearms having such gas tubes are susceptible to various drawbacks.
When improperly oriented relative to the action, such systems can result in weapon disturbance due to balance shifting during the action cycle and can undesirably increase the weight of the resultant weapon. Further, being exposed to the discharge gases, such gas tubes can achieve operating temperatures that could burn the user if the user inadvertently contacts the gas tube after even short periods of operation of the firearm. To improve heat dissipation, such gas tubes are commonly exposed to atmosphere and formed as generally round tubular structures oriented along the upper surface of the barrel proximate a forward facing end of the receiver which supports the action of the firearm. In many configurations, a piston, tappet, connecting rod, or portion of a bolt carrier slideably cooperates with at least a portion of a chamber or passage defined by the gas tube. The desired cyclic operation of the firearm requires a generally coaxial alignment of the piston or the structure that is intended to be translated by the gas stream and the chamber or passage of the gas tube to maintain the generally slideable cooperation of the piston or bolt carrier and at least a portion of the gas tube. That is, a less than desired alignment between the gas tube assembly and the receiver assembly can result in jamming of the action and/or the piston during operation of the firearm due to misalignment and/or premature degradation of firearm action lubrication.
Unfortunately, the connection methodology associated with securing the gas tube assembly relative to the receiver assembly commonly provides a singular interface wherein the gas tube is either secured relative to the receiver assembly or removable therefrom. Such connection methodologies require generally exact machining tolerances to achieve and maintain the desired alignment of gas tube assembly and the receiver assembly during operation of the firearm. Such tolerances increase the cost associated with manufacturing such firearms and detract from serviceability of the same.
Such gas tube assemblies also commonly have a generally round exterior profile and extend a significant distance forward of an upper portion of the forward end of the receiver. The shape and location of the gas tube relative to the receiver complicates the ability to secure accessories such as sighting and light accessories relative to the underlying firearm. Unfortunately, the location of the gas tube relative to the underlying firearm at a location forward of the receiver and generally above the barrel is the same location that many users would prefer to secure to accessories, particularly sighting accessories, relative to the underlying firearm. That is, when engaged with the firearm, the longitudinal distance associated with the gas tube is commonly directly below the line of sight associated with the desired operation of the firearm and at a location between the eye of the user and a muzzle of the firearm that is more desirable for the mounting of sighting optics, lights, and the like. Unfortunately, accommodating the gas tube with the desired spacing to adjacent structures complicates the ability to secure such accessories to the underlying firearm at the more desirable locations.
Therefore, there is a need for a firearm gas tube assembly and firearms having a gas tube assembly that can be secured in the underlying firearm in an adjustable manner to achieve and maintain the desired alignment of the gas tube assembly and the receiver assembly to maintain the desired repeatable and cyclic operation of the underlying firearm. There is a further need for a firearm gas tube assembly that can accommodate greater deviation associated with the desired cooperation of the gas tube assembly and the associated receiver assembly. There is a further need for a firearm gas tube assembly that facilitates expedient and convenient securing of accessories such as sighting devices relative to the underlying firearm.